1. Field of the Invention
The present invention relates to a drive system for a turbocharger with a rotary electric motor/generator "machine" in general, and more particularly, to a drive system which can easily generate a phase of an initialized position to be supplied to a driving AC electric power source of the AC motor/generator.
2. Description of the Related Art
In recent years, there have been proposed various systems for recovering exhaust energy by transforming rotary force of an exhaust turbine into electric power energy. Japanese Laid-Open Patent Publication No. 63-30213 discloses, as one such system, a system for a turbocharger with a rotary electric machine having a turbine rotatable by the energy of exhaust gases emitted from an internal combustion energy and a compressor coupled directly to the turbine, for compressing intake air and supplying compressed intake air to the engine. An AC motor coupled directly to the rotatable shaft of the turbine operates at times as a generator, and exhaust energy obtained from the turbine through the AC motor is recovered as DC electric power for the generated electric power. When the engine operates at low speeds, the exhaust gases emitted from the engine are under lower pressure and turbocharged pressure from a compressor to the engine declines. At this point recovered and stored DC electric power is converted into AC electric power by an inverter. For operating the engine, the AC voltage is applied to the AC motor/generator, which assists in the rotation of a compressor for obtaining necessary supercharged air.
The above drive system for a turbocharger with the rotary electric machine has small magnet pieces mounted on an initialized position of the back side of compressor impeller and has a picking-up coil mounted on the turbine housing opposite the permanent magnet pieces. When an AC motor generator operates as a motor, polyphase current is generated and supplied to the AC motor generator. The polyphase current corresponds to a signal of initialized position supplied from a position sensor which is composed of the above permanent magnet pieces and the coil. That is, a frequency of supplied electric power is read with a pulse interval of a signal of initialized position from the positional sensor. Then a first phase starts, as the signal of initialized position functions as a trigger. Successively, other phases start at predetermined phase differences.
Since a positional adjustment between the mechanically rotary initialized position of a positional sensor and an electrically initialized position of phase is only executed when the system and the turbocharger with the rotary electric machine are newly loaded on a vehicle, or when a portion of the turbocharger with the rotary electric machine or the drive system are replaced, position adjustment is not achieved when a motor vehicle is operating.
A rotor of the AC motor generator is screwed on a rotational shaft, and since the rotational speed of the rotational shaft reaches nearly 200,000 rpm, the rotor may get out of position (slip). When the rotor gets out of the position, it brings about not only inefficient operation but also damage of the inverter. In addition, every replacement of the turbocharger with the rotary electric machine and the system for driving requires time for the positional adjustment.